This invention relates to electrolytic cells for the manufacture of halogen or halates from their corresponding brine electrolytes.
An electrolytic cell of the general type to which this invention relates is illustrated in U.S. Pat. Nos. 3,824,172 and 4,075,077.
More particularly, the cell of this invention includes an improved, novel anode that is constructed of an aluminum-titanium composite material to provide a lightweight, inexpensive, highly conductive critical component for a cell which will operate at high amperage and low to medium current density to produce a greater amount of halogen or halate product at a lower power consumption than a comparable cell utilizing prior art solid titanium anodes.
Typical electrolytic cells for halogen and halate production comprise solid titanium plates disposed between cathode plates.
Titanium has been employed in the past as the anode base or core because of its high resistance to the electrolyte brine solution. However, because of the tendency of a non-conducting oxide film to form on the titanium surface in the brine, a precious metals coating in the instant invention is applied over the outer surface of the titanium anode to prevent the film formation and provide a highly conductive surface. If the highly conductive precious metal coating over the anode wears through during operation of the cell, the titanium base assures that the anode structure will not erode further.
Aluminum has not been used heretofore as an anode core material because it is incompatible with the cell environment, i.e, the brine electrolyte and halogen or chlorate product within the operating cell. Aluminum would otherwise be a desirable anode material as it is highly electroconductive, lightweight, and relatively inexpensive. Aluminum cored, titanium sheathed conductors positioned outside the cell environment of electrolytic cells are known and are shown, for example, in U.S. Pat. No. 3,857,774. However, an aluminum containing anode wherein the aluminum component is immersed in the brine electrolyte of the cell has heretofore not been utilized.
In the present invention submerged gaskets in electrolyte solution have been eliminated. Such prior art submerged gaskets have presented a serious source of problems. Moreover, the present invention eliminates the normal steel corrosion that occurs in conventional cells at the gas-liquid interface of the cell interior. Such corrosion is eliminated with the use of titanium explosive bonded to the steel flange which is welded to the container wall. The titanium bonding extends into the interior of the container to a point at least below the normal electrolyte fluid level, thereby completely submerging the steel in the cell liquid where it is cathodically protected from corrosion. In the area of normal maximal corrosion at the gas-liquid interface titanium is in contact with the electrolyte, thereby eliminating the corrosion.
Because the titanium is operating as a cathode, a special alpha form of titanium, which is extremely low in iron content, is used as such low iron content titanium is relatively immune to the normal cathodic corrosion exhibited by titanium. The titanium head is welded to the flange which makes a continuous gasket free system. The only gaskets are the electrically insulating gaskets between the cover and the head-container assembly which is a relatively problem free area for such a gasket.
In the present invention, because the current is conducted through the thickness of the titanium which is usually in the order of 0.030 inches or less, there is a negligible effect on the voltage of the cell. The entire aluminum or copper structure is available as the active anode. Accordingly, at comparable current density, the cell of this invention consumes sufficiently less power than the standard prior art anode design of earlier cells.